1. Field of the Invention
The present invention relates to an image display apparatus that can repeatedly execute displaying and erasing operations of images by allowing display particles to move in an electric field and such display particles used for the display apparatus.
2. Description of the Related Art
Conventionally, an image display apparatus that displays images by moving display particles in a gaseous phase has been known. The image display apparatus has a structure in which display particles in a powder state are sealed between two substrates at least one of which is transparent, and by generating an electric field between the substrates, the display particles are moved and adhered to one of the substrates so that an image is displayed. Upon driving such an image display apparatus, a voltage is applied between the substrates to generate an electric field, and the display particles are moved along the electric field direction so that by selecting the electric field direction on demand, the displaying and erasing operations of images can be executed repeatedly. For this reason, in the image display apparatus, there have been strong demands for reducing adhesive force of the display particles to the display particle contact surfaces between the substrates.
As the display particles for use in an image display apparatus, particles obtained by coating a surface of each of base particles containing a binder resin and a colorant with inorganic fine particles such as hydrophobic silica and hydrophobic titania by a dry mixing method using a Henschel mixer or the like, have been known (Japanese Patent Application Laid-Open No. 2004-29699). However, since such a dry mixing method fails to completely coat the surface of each of base particles, it is not possible to allow the fine particles to sufficiently exert an adhesive force reducing effect. Consequently, upon carrying out repetitive driving operations, degradation of contrast occurs between an image portion and a non-image portion.
Therefore, a technique has been proposed in which, after an inorganic layer has been formed on the surface of each of base particles by using a wet synthesizing method, a surface treatment is carried out thereon so that contrast durability can be improved (Japanese Patent Application Laid-Open Nos 2003-167277 and 2006-72345). As the material for forming such an inorganic layer in the wet synthesizing method, metal tetraalkoxides such as tetraethoxysilane, tetramethoxysilane, tetraethoxy titanium and tetramethoxy titanium, are used.
However, in an attempt to further improve the contrast durability, it is not possible to sufficiently prevent degradation of contrast upon carrying out repetitive driving operations, even by the use of such display particles. For example, after repetitive driving operations of 30,000 times, cracks occur in the inorganic layer to cause a film separation. This causes the surface of the base particle to be exposed, resulting in degradation of contrast.
It is an object of the present invention to provide display particles and an image display apparatus that can sufficiently prevent degradation of contrast at the time of repetitive driving operations for a long period of time.